www-content/pages/docs/efl/start.txt

~~Title: EFL~~
~~CODE-c~~

{{page>index}}

==== EFL ====

EFL is a range of libraries that cover APIs to solve every day
problems we, and others have encountered. You can see it having
various API layers, with some intended for very low-level controls and
access that no one but specialists (eg writing a window manager
itself) will need, through to higher level "just writing a notepad"
application. The lower you go, the less portable things can be. Here
we will cover the EFL features and APIs used to make things portably
and cleanly. We will cover these topics here:

  * Data structures (lists, hash tables, growable buffers/strings etc.)
  * Main loop event, I/O and timing core
  * Event queue and call handling
  * Canvas scene graph and rendering
  * UI object element layout, animation and theme abstraction
  * Widgets/controls (buttons, sliders, scrollers etc.)
  * Input method framework
  * Data archive storage & retrieval
  * Data structure (de)serialization
  * Video & audio codec playback, control and display
  * IPC and network connectivity (TCP, UDP, unix domain & abstract sockets, HTTP)
  * File utilities
  * Freedesktop.org standards (desktop files, menus, mime types, icons)
  * Async I/O
  * D-Bus IPC integration
  * Location API
  * Basic Audio playback, recording and mixing

You will use a range of libraries to make use of the above, and so
learning the naming of these is important to know where to look. They
will be in Ecore, Evas, Edje, Elementary (Elm), Ecore_IMF, Eet,
Emotion, Ecore_Con, Ecore_IPC, Eio, Eldbus, Elocation, Ecore_Audio,
Ecore_File and Efreet.

We will make an assumption that you have a reasonable grasp of the C
programming language here. Perhaps you might want to read
[[http://www.cprogramming.com/tutorial/c-tutorial.html|this C introduction tutorial]]
if you are new to C, or need a refresher.

----

=== Application Mainloop ===

It is assumed every application has a [[mainloop]], and that EFL is
in charge of that. If you are writing a library, then that assumption
would be made ultimately of the application using that library as well.
For the purposes of this introduction to EFL, we will talk about an
application, how it starts, runs and shuts down.

Every application is expected to have a life-cycle as follows. If you
have a design that is significantly different then you will be
struggling against EFL and what it is pushing you to use. This does
not mean we do not support threads, we just push you into a specific
design pattern.

{{ :docs:efl:mainloop.svg?nolink |Application Mainloop}}

An application would spend almost it's entire life inside the
[[mainloop]] sleeping, processing events and then updating it's UI,
until it decides to exit. All of this would take place inside the
[[mainloop]] processing function elm_run() which will only return
once the [[mainloop]] voluntarily exits if an elm_exit() function is
called while it runs, which marks the loop to exit, next time it has a
chance. Before and after this, will be initialization and shutdown of the
application. Your most basic application that just does nothing but
wait forever for events would be:

<code c example.c>
#include <Elementary.h>

EAPI_MAIN int
elm_main(int argc, char **argv)
{
   elm_run();
   return 0;
}
ELM_MAIN()
</code>
Compile it (and other examples on this page) with:
  cc example.c -o example `pkg-config --cflags --libs elementary`

Expanding on this, let us make our first application with an actual
visible window and a button inside to click to exit:

<code c example.c>
#include <Elementary.h>

static void
on_click(void *data, Evas_Object *obj, void *event_info)
{
   evas_object_del(data);
}

EAPI_MAIN int
elm_main(int argc, char **argv)
{
   Evas_Object *win, *btn;

   elm_policy_set(ELM_POLICY_QUIT, ELM_POLICY_QUIT_LAST_WINDOW_CLOSED);

   win = elm_win_util_standard_add("Main", "Hello, World!");
   elm_win_autodel_set(win, EINA_TRUE);

   btn = elm_button_add(win);
   elm_object_text_set(btn, "Goodbye Cruel World");
   elm_win_resize_object_add(win, btn);
   evas_object_smart_callback_add(btn, "clicked", on_click, win);
   evas_object_show(btn);

   evas_object_show(win);

   elm_run();

   return 0;
}
ELM_MAIN()
</code>

When the application runs, the ELM_MAIN() macro sets up a normal
main() function, inits EFL for you and then calls elm_main() with
the usual application argc & argv parameters you get in C. When
elm_main() returns, it will pass the return value to the return
value of main() for the application exit code. Before it does this,
EFL will be cleanly shut down for you. You are encouraged to use this
setup above to ensure this happens.

<code c>
elm_policy_set(ELM_POLICY_QUIT, ELM_POLICY_QUIT_LAST_WINDOW_CLOSED);
</code>

The first thing we do is enable a policy where if our last window is
deleted, the [[mainloop]] started by elm_run() is automatically
quit when this last window is closed. This is really handy for
applications with multiple windows that want to just go away when they
are no longer presenting any UI.

<code c>
win = elm_win_util_standard_add("Main", "Hello, World!");
</code>

We now create a standard window with a standard background using a
utility function. It has the **name** set to "Main". This is normally
not a user-visible property of a window. It is used to identify that
window separately from other windows the app may create. A dialog, a
file selector window, a settings dialog etc. so name appropriately
here. The window will display a title of "Hello, World!" in the
titlebar (if such a thing exists on your platform). This title may be
used in other places on a platform such as a window switcher, a
taskbar or some other interface control element. The window will have a
background already placed as the resize object of a window.

<code c>
elm_win_autodel_set(win, EINA_TRUE);
</code>

Next we enable **autodel** on the window. This means that if someone
hits the close button, or otherwise uses some normal environment
mechanism (keybinding, menu) to close the window, the window object is
automatically deleted on the application side. If you do not do this,
these mechanisms will not work and the window will stay around. It is
expected that you would add a callback to handle the "delete,request"
event on the window and then either delete it or do something like
prompt the user if they are sure they wish to close the window
(unsaved content?) etc.

<code c>
btn = elm_button_add(win);
</code>

Next we create a button (relative to the window). You must create all
objects relative to some object inside a window or the window itself.
All graphical objects belong to a window of some sort. This will not
have set up the parent/child containering and control relationships
yet. That comes later.

<code c>
elm_object_text_set(btn, "Goodbye Cruel World");
elm_win_resize_object_add(win, btn);
</code>

We now set the label of the button to "Goodbye Cruel World", then add
the button as a window resize object. If we did not set the label
text, the button would be empty (and quite small by default). Windows
have a special list of resize objects (can be more than one) stacked
one on top of the other which resize when the window resizes. In turn
they also affect the window sizing with their minimum and maximum
sizes as well as sizing hints for weight and alignment (which we will
come to later).

<code c>
static void
on_click(void *data, Evas_Object *obj, void *event_info)
{
   evas_object_del(data);
}
</code>
<code c>
evas_object_smart_callback_add(btn, "clicked", on_click, win);
</code>

We now add a callback for the "clicked" smart event on the button.
This will call the ''on_click'' function when a user clicks on the
button. The [[mainloop]] drives event handling and thus calling of
this callback. All event callbacks can pass in an arbitrary pointer to
anything the like. This will be passed as the first data pointer to
the callback above. In this case we will passing our window pointer as
we want to delete the window when someone presses the button. Due to
our policy settings, this will end up deleting the last window we have
and automatically exiting the [[mainloop]], and then of course the
application. The example works this way to show how it might be
extended to open multiple windows and only have the window you click
the button in be deleted, until all windows are gone and application
cleanly exits.

<code c>
evas_object_show(btn);
</code>

Next we show the button. All graphical objects are hidden by default.
This avoids unwanted events like mouse in, move and out events due to
objects being created underneath the current pointer position. It
makes things more efficient as you can show the object after you have
finished defining its state.

<code c>
evas_object_show(win);
</code>

Now we show the window. It is best to show it last just before you
jump into the [[mainloop]] to process everything. This means all
window setup is invisible until it is finished.

<code c>
elm_run();
</code>

Finally we begin the [[mainloop]]. This function will not exit until
the [[mainloop]] is done and exits (with an elm_exit() being
called from inside some callback there). So at this point your
application is handing full control over it's execution to EFL and the
[[mainloop]] to deal with events and rendering of updates. From inside the mainloop function run by EFL, all your callbacks (functions you register to be called when events, state changes etc. etc. happen) will be called.

----

**NOTE**: If you don't want to use ELM_MAIN(), you can use
elm_init() and elm_shutdown() manually yourself. You **MUST**
call elm_init() before you call any EFL functions. It could fail
too. Also never call any EFL functions after elm_shutdown().

<code c example.c>
#include <Elementary.h>

int
main(int argc, char **argv)
{
   if (!elm_init()) return -1;

   elm_run();

   elm_shutdown();
   return 0;
}
</code>

----

~~DISCUSSIONS~~